This invention relates generally to substrates used in making articles such as training pants, diapers, feminine hygiene products, incontinence garments and the like, and more particularly to such substrates having graphics thereon.
Personal wear articles find widespread use as personal care products including, without limitation, diapers, children's toilet training pants, adult incontinence garments, sanitary napkins and the like, as well as surgical bandages and sponges. Certain such articles are generally considered to be disposable in that they are usually intended to be discarded after a limited period of use, i.e., the articles are not intended to be laundered or otherwise restored for reuse. Disposable absorbent articles typically comprise an absorbent body disposed between a liner, which contacts the wearer's skin, and an outer cover, which inhibits liquid body waste absorbed by the absorbent body from leaking out of the article. The liner of the absorbent article is typically liquid permeable to permit liquid body waste to pass therethrough for absorption by the absorbent body.
Conventional absorbent articles also typically include some type of fastening system for securing the absorbent article in an assembled configuration and/or for fitting the article on the wearer, such as on the wearer's waist in the case of diapers and training pants. In many such applications, the fastening system is releasable and refastenable so that the article can be temporarily removed and then refastened to the wearer.
It is further known to apply a graphic, such as in the form of a character, fabric pattern, undergarment markings, object and/or alphanumeric (e.g., numbers, words, phrases, instructions, etc.) to personal wear articles to enhance the aesthetic or otherwise visual appearance or usefulness of the article. Graphics applied to such articles may also provide visual assistance to the wearer or to a caregiver securing the article on the wearer. In some instances, the graphics may include a material or substance capable of being visible in low light conditions, including in the dark, to further enhance the appeal to the wearer or ease of use by the caregiver.
One common technique used to apply a graphic to a personal wear article, and more particularly to the outer cover thereof, is commonly known as flexographic printing and provides a cost effective, high speed, high quality printing technique for printing thin films or non-woven fibrous webs while maintaining the tactile softness of the film or web. Flexography involves the use of flexible, raised rubber or photopolymer print plates to carry an image to a given substrate onto which the graphic is transferred. More specifically, an anilox roll is rotated through an ink reservoir to become coated with ink and then further rotated into contact with a print cylinder on which the print plate is mounted. The ink is transferred from the anilox roll onto the print plate. The print cylinder rotates relative to an impression cylinder over which the substrate moves whereby the ink covered print plate presses against the substrate (and impression cylinder) to transfer the ink from the print plate to the substrate to create the desired graphic.
It is becoming more desirable that absorbent articles appear more like conventional garments. For example, children's toilet training pants desirably appear more similar to conventional children's cloth underpants. One feature that would facilitate such an improved appearance is brighter, more vibrant graphics on absorbent articles. Compared to graphics on printed cloth underpants, flexographic printed non-woven substrates incorporated into training pants yield a visually dull graphic. It is also common to print graphics on a film layer that is then overlaid by a non-woven layer (e.g., to provide a softer, more cloth-like feel and appearance). However, covering the film layer also tends to dull the graphics imprinted on the film layer.
One readily apparent approach to improve the vibrancy of the graphics applied by flexographic printing to non-woven webs would be to increase 1) the volume of ink held by the anilox roll and 2) to increase the impression pressure of the print cylinder (i.e., the pressure applied by the print cylinder against the impression cylinder). That is, by increasing the ink volume and pressing the print plate harder against the substrate, it is expected that the vibrancy of the graphic would increase. While such process changes can improve printed graphic vibrancy, increased impression pressure, by itself, does not yield a significant improvement in vibrancy. Moreover, too much impression pressure can distort the graphic. Increasing the ink volume on the anilox roll also does not yield significant improvement of the graphic vibrancy. Specifically, solely increasing the volume of ink on the anilox roll does not translate into a greater volume of ink transferred to the non-woven substrate to increase the vibrancy of the graphic.
It is also known that printing vibrant images on polyolefin fibrous non-woven webs, and in particular those made from polypropylene fibers, is difficult.
There is a need, therefore, for high vibrancy graphics applied to non-woven substrates (e.g., having irregular surfaces), particularly by flexographic printing. More particularly, it is desirable that such high vibrancy graphics be achieved with a relatively thin layer of ink applied to the non-woven substrate to thereby maintain the soft, clothlike texture of the non-woven substrate. There is also a need to improve the vibrancy of graphics on absorbent articles while maintaining or improving the cost efficiency associated with the manufacture of such articles.